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                                                                    EXHIBIT 5.01


                                October 15, 1999



HNC Software Inc.
5935 Cornerstone Court West
San Diego, CA  92121-3728

Gentlemen/Ladies:

         At your request, we have examined the Registration Statement on Form
S-8 (the "REGISTRATION STATEMENT") to be filed by you with the Securities and
Exchange Commission (the "COMMISSION") on or about October 15, 1999, in
connection with the registration under the Securities Act of 1933, as amended,
of an aggregate of 250,000 shares of your Common Stock (the "STOCK"), all of the
Stock is subject to issuance by you upon the exercise of a stock option granted
by you outside of any of your stock option plans (the "NON-PLAN OPTION").

         In rendering this opinion, we have examined the following:

         (1)      Your registration statement on Form S-1 (Registration Number
                  33-91932) filed with and declared effective by the Commission
                  on June 20, 1995, together with the Exhibits filed as a part
                  thereof;

         (2)      your registration statement on Form 8-A filed with the
                  Commission on May 26, 1995, together with the order of
                  effectiveness issued by the Commission therefor on June 20,
                  1995;

         (3)      the Registration Statement, together with the Exhibits filed
                  as a part thereof, including without limitation the
                  Non-Qualified Stock Option Agreement between you and Mr. Ward
                  Carey (the "NON-PLAN OPTION AGREEMENT");

         (4)      the prospectus prepared in connection with the Registration
                  Statement;

         (5)      the minutes of meetings and actions by written consent of the
                  stockholders and Board of Directors that are contained in your
                  minute books that are in our possession;

         (6)      the stock records that you have provided to us (consisting of
                  a certificate from your transfer agent of even date herewith
                  verifying the number of your issued and outstanding shares of
                  capital stock as of October 14, 1999, and a list of option
                  and warrant holders respecting your capital stock and of any
                  rights to purchase capital stock that was prepared by you and
                  dated October 15, 1999, verifying the number of such issued
                  and outstanding securities);

         (7)      a Management Certificate addressed to us and dated of even
                  date herewith executed by the Company containing certain
                  factual and other representations;


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         (8)      The Nasdaq National Market Listing of Additional Share
                  Notification prepared in connection with the Registration
                  Statement; and

         (9)      the Restated Certificate of Incorporation of the Company filed
                  with the Delaware Secretary of State on June 13, 1996 and the
                  Bylaws of the Company, both as filed by the Company with its
                  Report on Form 10-Q for the quarter ended June 30, 1996.

         In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity of all documents submitted to us as
originals, the conformity to originals of all documents submitted to us as
copies, the legal capacity of all natural persons executing the same, the lack
of any undisclosed terminations, modifications, waivers or amendments to any
documents reviewed by us and the due execution and delivery of all documents
where due execution and delivery are prerequisites to the effectiveness thereof.

         As to matters of fact relevant to this opinion, we have relied solely
upon our examination of the documents referred to above and have assumed the
current accuracy and completeness of the information obtained from records
referred to above. We have made no independent investigation or other attempt to
verify the accuracy of any of such information or to determine the existence or
non-existence of any other factual matters; however, we are not aware of any
facts that would cause us to believe that the opinion expressed herein is not
accurate.

         We are admitted to practice law in the State of California, and we
express no opinion herein with respect to the effect of the laws of any
jurisdiction other than the existing laws of the United States of America, the
State of California and the State of Delaware.

         Based upon the foregoing, it is our opinion that the 250,000 shares of
Common Stock that may be issued and sold by you upon the exercise of the
Non-Plan Option, when issued and sold in accordance with the Non-Plan Option
Agreement, will be validly issued, fully paid and nonassessable.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto.

         This opinion speaks only as of its date and we assume no obligation to
update this opinion should circumstances change after the date hereof.



                                         Very truly yours,

                                         /s/ FENWICK & WEST LLP









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